A parallel optical communications module is an optical communications module that has multiple transmit (TX) channels, multiple receive (RX) channels, or both. A parallel optical transceiver module is an optical communications module that has multiple TX channels and multiple RX channels in the TX and RX portions, respectively, of the module. A parallel optical transmitter module is an optical communications module that has multiple TX channels, but no RX channels. A parallel optical receiver module is an optical communications module that has multiple RX channels, but no TX channels.
The TX portion of a parallel optical transceiver or transmitter module comprises components for generating modulated optical signals, which are then optically coupled by an optics system of the module into the ends of respective optical fibers and transmitted over an optical link or network. The TX portion typically includes laser diode or light emitting diode (LED) driver circuitry and a plurality of laser diodes or LEDs. The driver circuitry outputs electrical signals to the laser diodes or LEDs to modulate them. When the laser diodes or LEDs are modulated, they output optical signals that have power levels corresponding to logic 1s and logic 0s. The optics system of the module directs the optical signals produced by the laser diodes LEDs into the ends of respective optical fibers, which are typically held within an optical connector that mates with the parallel optical transceiver or transmitter module.
The RX portion of a parallel optical transceiver or receiver module includes a plurality of receive photodiodes that receive incoming optical signals output from the ends of respective optical fibers, which are typically held in an optical connector that mates with the parallel optical transceiver or receiver module. The optics system directs the light that is output from the ends of the optical fibers onto the respective photodiodes. The photodiodes convert the incoming optical signals into electrical analog signals. An electrical detection circuit, such as a transimpedance amplifier (TIA), receives the electrical signals produced by the photodiodes and outputs corresponding amplified electrical signals, which are processed by other receiver circuitry in the RX portion to recover the data.
A mid-plane mounting configuration for a parallel optical communications module is one in which the module is mounted on the surface of a host printed circuit board (PCB). A typical mid-plane mounting configuration includes an LGA socket that is mounted on the host PCB and a parallel optical communications module that is mounted in the socket. The LGA socket has a bottom and typically has side walls. Arrays of electrical contacts are disposed on upper and lower surfaces of the bottom of the socket. The parallel optical communications module has a module PCB having an array of electrical contacts disposed on its lower surface. The electrical contacts on the lower surface of the module PCB electrically connect with respective electrical contacts of the array disposed on the upper surface of the socket when the module is mounted on the socket.
The LGA socket is typically secured to the upper surface of the host PCB by drilling holes through the host PCB and inserting fastening devices (e.g., screws) through the holes formed in the host PCB and through holes formed in the socket to fasten the socket to the host PCB. After the socket has been secured to the host PCB, the optical communications module is mounted on the socket such that the array of electrical contacts disposed on the lower surface of the module is electrically connected to the array of electrical contacts disposed on the upper surface of the bottom of the socket. The LGA socket locates, compresses and holds the optical communications module in a fixed position on the host PCB and electrically interfaces the electrical contacts disposed on the lower surface of the module PCB with respective electrical contacts disposed on the upper surface of the host PCB.
A backing plate is often secured to the backside of the host PCB and is mechanically coupled to the LGA socket to provide support for the host PCB at the mounting location. A similar plate is often secured to the front side of the host PCB and used as a cover to maintain a flat profile for the mounted configuration of the module within the LGA socket. These plates are typically secured to the host PCB by screws or similar fastening devices.
Securing the socket to the host PCB in this manner reduces mechanical shocks and vibrations to the module that could otherwise damage the module or detrimentally affect its performance due to loss of connectivity between socket and module. One of the problems associated with securing the socket to the host PCB in this manner is that electrical conductors of the host PCB (i.e., vias and traces) cannot be routed through the locations where the holes have been drilled in the host PCB. This presents challenges when it comes to designing the routes of the host PCB. Another problem is that the LGA sockets often are relatively expensive, large in size, and have to be hand-assembled (e.g., drilling holes, soldering, attaching plates, etc.), which leads to a mid-plane mounting solution that is relatively expensive and time consuming to implement.
A need exists for an LGA for mid-plane mounting a parallel optical communications module on a host PCB that eliminates the need for the socket, thereby reducing cost, size and the need to perform a large number of assembly operations by hand.